Upper Motor Neuron Lower Motor Neuron

David Brewer DVM, DACVIM (Neurology)

Objectives

• Fundamental differences between the UMNand LMN systems

• Typical symptoms seen with dysfunction• Role in neurolocalization

• Cases examples

UMN? LMN? Who Cares?

• Localization

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Definitions

• UMN- The neurons of the brain that control motor activity of the body

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Definitions

• UMN- Cell bodies arelocated in the cerebrumand brainstem

• Entire UMN is confinedto CNS

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Definitions • LMN- the neurons that directly innervate

the muscles.

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Definitions • LMN- Cell bodies are located in the ventral

gray horn of the spinal cord

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Functions • UMN

• ‘Tells’ the LMN what to do • Stimulate or inhibit the LMN • Initiation of voluntary

movement • Maintenance of muscle

tone and support against gravity

• Regulation of posture

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Functions • LMN-

• Receives inputs from the UMN

• Connects the CNS with the muscles

• Spinal reflexes

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Dysfunction of the UMN • Paretic (weakness) to paralysis • Gait: (if still walking)

• Long strided • Crossing • Scuffing

• Loss of inhibition: • Spasticity • Hyperreflexia / hypertonia /

abnormal reflexes • Abnormal postures (brain lesion)

• Ex. opisthotonus

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UMN Ataxia

Dysfunction of the UMN

• Gait Generation ▪ Dogs/cats- brainstem ▪ People- cerebrum

Romy

Romy

Romy

Romy

Loss of Inhibition 1.Gravity (pleximeter) stimulates muscle spindle 2. Firing along Ia afferent 3. Stimulation of alpha motor neuron and muscle contraction ** Must be controlled by UMN system

Tonic Gamma Loop Mechanism 2

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Crossed Extensor Reflex

Dysfunction of the LMN • Paretic (weakness) to paralysis • Gait: (if still walking)

• Short-strided • Choppy • Lame

• Hypotonia • Hyporeflexive • Rapid muscle atrophy

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Postural Reactions

• Both UMN and LMN lesions can cause abnormal postural reactions

• More so with UMN • Depends on severity

Goal: • How do we use UMN and LMN

symptoms to help localize a lesion?

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Neurolocalization

Goal: Neurolocalization

• The location of the lesion along the neuroaxis will determine which limbs are affected ▪ UMN symptoms will be present in limbs

downstream from a CNS lesion ▪ LMN symptoms will only be present if the

motor nerve or the intumescence is affected

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Goal: Neurolocalization

• Symptoms can be isolated to one limb or generalized to all limbs.

• Not every symptom needs to be present to localize a region

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Brain C1-C5 C6-T2 T3-L3 L4-S3 Diffuse LMN

TL UMN UMN LMN Normal Normal LMN

PL UMN UMN UMN UMN LMN LMN

UMN or LMN Bladder?

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Brain C1-C5 C6-T2 T3-L3 L4-S3 Diffuse LMN

TL UMN UMN LMN Normal Normal LMN

PL / Bladder UMN UMN UMN UMN LMN LMN

Bladder

• UMN Bladder ▪ Seen with lesions cranial

to L4 ▪ Loss of inhibition causes

excess tone on the urethral sphincters

▪ Large difficult to express ▪ Overflow incontinence

UMN Bladder Treatment

• Relax Internal Urethral Sphincter ▪ Alpha-adrengeric antagonist ▪ Ex. Phenoxybenzamine or Prazosin

• Relax External Urethral Sphincter ▪ Skeletal muscle relaxant ▪ Ex. Diazepam

Bladder • LMN Bladder ▪ Seen with lesions caudal

to L4 ▪ Hypotonia of the

urethral sphincters ▪ Fills partially ▪ Continuous dribbling ▪ Easy to express

LMN Bladder Treatment

• Promote Bladder Contraction ▪ Stimulate muscarinic receptors

• Ex. Bethanechol

Technically Speaking

• LMN is referencing just the nerve

• What about the muscle or the junction between the nerve and muscle?

Neuromuscular System

• LMN (Neuropathy) • Muscle (Myopathy) • NMJ (Junctionopathy)

Neuromuscular System

Myopathy Neuropathy NMJ

Muscle mass/tone Normal to ↓ ↓ Normal

Gait Paresis Paresis Paresis may be episodic

Postural Reactions Normal ↓ Normal

Reflexes Normal ↓ Normal

Case Example 1

• Middle-age German Shepherd • CC: Wobbly in the pelvic limbs

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Brain C1-C5 C6-T2 T3-L3 L4-S3 Diffuse LMN

TL UMN UMN LMN Normal Normal LMN

PL / Bladder UMN UMN UMN UMN LMN LMN

Differentials

• C6-T2 myelopathy ▪ Degenerative - IVDD ▪ Anomalous – Wobbler’s syndrome ▪ Metabolic - ?? ▪ Neoplastic- Extradural or intramedullary ▪ Inflammatory- Immune-mediated or infectious ▪ Traumatic / Toxic- Contusion ▪ Vascular- FCE

Diagnostics

Diagnosis

• C6-T2 myelopathy

▪ Anomalous – Wobbler’s syndrome

Treatment and Outcome

• Treatment ▪ Owner elected conservative management

• Outcome ▪ Fair to good response to prednisone and life

long gabapentin

Case Example 2

• Young Bichon • CC: Down in pelvic limbs

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Brain C1-C5 C6-T2 T3-L3 L4-S3 Diffuse LMN

TL UMN UMN LMN Normal Normal LMN

PL / Bladder UMN UMN UMN UMN LMN LMN

Differentials

• T3-L3 myelopathy ▪ Degenerative - IVDD ▪ Anomalous – Malformation, cyst ▪ Metabolic - ?? ▪ Neoplastic- Extradural or intramedullary ▪ Inflammatory- Immune-mediated or infectious ▪ Traumatic- Contusion ▪ Vascular- FCE

Diagnostics

Diagnosis

• T3-L3 myelopathy ▪ Degenerative - IVDD

Treatment and Outcome

• Treatment ▪ Hemilaminectomy

• Outcome ▪ Normal at 6 weeks post surgery

Case Example 3

• Young adult Giant Schnauzer • CC: Down in all 4

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Brain C1-C5 C6-T2 T3-L3 L4-S3 Diffuse LMN

TL UMN UMN LMN Normal Normal LMN

PL / Bladder UMN UMN UMN UMN LMN LMN

Differentials

• Diffuse LMN Disease ▪ Degenerative – Hereditary?, Storage diseases ▪ Anomalous – ? ▪ Metabolic – Endocrine (DM, cortisol, thyroid) ▪ Neoplastic- Lymphoma, paraneoplastic ▪ Inflammatory- Polyradiculoneuritis, infectious – protozoal,

(botulism) ▪ Traumatic / Toxic- (Tick paralysis) ▪ Vascular- ?

Diagnostics

Diagnostics

• CBC – Normal • Chem – Normal • Urinalysis – Normal • 3 view chest radiographs – Normal • Abdominal Ultrasound – Normal • Baseline cortisol and T4 – Normal

Additional Diagnostics

• Electrodiagnostics ▪ Electromyography ▪ Motor Nerve Conduction Velocity ▪ F-Waves

• +/- Muscle nerve biopsy

Updated Differentials

• Diffuse LMN Disease ▪ Degenerative – Hereditary?, Storage diseases

▪ Neoplastic- Lymphoma, paraneoplastic ▪ Inflammatory- Polyradiculoneuritis, infectious – protozoal,

(botulism) ▪ Traumatic / Toxic- (Tick paralysis)

Treatment and Outcome

• Treatment ▪ Frontline application

• Outcome ▪ ~2 weeks later – 90% ▪ ~4 weeks later – 100%

Presumptive Diagnosis

• Diffuse LMN Disease

▪ Inflammatory- Polyradiculoneuritis,

Case Example 4

• 2 yr old Newfoundland • CC: Unable to walk

Case Example 4

Take Home Points

• UMN disease should have distinctly different signs from LMN disease • Cervical spinal cord disease and diffuse LMN disease can sometimes be

confused without thorough examination

• Diseases that affect the neuromuscular system can look very similar

• Gait evaluation is probably the most important aspect of the exam

• Acute localization is key!

QUESTIONS?